Welcome to MobileRead, paragme.
I'm sorry you haven't been able to get a response. I have the 505 but do not have experience with pdf. I actually avoid that format and only use epub, lrf, and lrx. Hopefully, someone with more experience with chime in.
The below link is to the PDF forums..
https://www.mobileread.com/forums/forumdisplay.php?f=184
If you browse through those threads you will probably note the varying opinions and comments on pdf usage / display on the 505. I know that there has been many comments about pdf tech books and usage on the 505 especially in the which one to buy threads.
Hopefully, the many member comments may help you determine if the 505 is really what you need.
The pdf doesn't preview on the Sony library (epub, lrf, and lrx will open in the Sony Library). You view the pdf with Adobe Reader and I am not sure if the view you see is what is displayed on the 505.
I hope this helps and if my information is incorrect someone will jump in and correct me
.